A widely used example of a developing method using a magnetic one-component developer is a magnetic non-contact developing method (for example, see PTL 1 and PTL 2).
With the magnetic non-contact developing method, a developing sleeve (a developer bearing member) accommodating a magnet bears a developer. A photoconductor is opposed to the surface of the developing sleeve with a predetermined minute gap therebetween, and the developer is splashed from the developing sleeve toward the photoconductor to perform developing. The developer in the developing unit is conveyed to the developing sleeve by a mechanical stirring mechanism or gravitation. The magnetic one-component developer is supplied to the developing sleeve with a fixed magnetic force of a magnet accommodated in the developing sleeve.
Another developing method using the magnetic one-component developer is a magnetic contact developing method (see PTL 3). This magnetic contact developing method has both of the characteristics of a non-magnetic contact developing method (for example, PTL 4) and the above magnetic non-contact developing method. The magnetic contact developing method forms an elastic layer on the surface of the developing sleeve to keeping the developing sleeve and the photoconductor in contact with each other in contrast to the above magnetic non-contact developing method. The magnetic contact developing method is also configured such that a magnet is disposed in the developing sleeve, and the developer is born on the surface of the developing sleeve by the magnetic force of the magnet, as with the non-magnetic contact developing method.
The magnetic non-contact developing method, which is generally employed when a magnetic one-component developer is used, holds a magnetic developer on the surface of the developer developing sleeve by the action of the magnetic force of the magnet accommodated in the developing sleeve. End sealing members are provided at both ends of the developing sleeve. The end sealing members seal gaps between the developing sleeve and the developing unit to prevent the developer from leaking outside the developing unit.
However, the action of the magnetic force of the magnet accommodated in the developing sleeve on the areas in which the end sealing members are provided may cause the developer to enter the gaps between the end sealing members and the developing sleeve. This developer may be firmly fixed to the developing sleeve between the end sealing members and the developing sleeve to form gaps between the end sealing members and the developing sleeve, thus causing developer leakage or the like. This is one of large technical problems due to the recent increase in the speed of image formation and the life of cartridges.
Furthermore, for the magnetic non-contact developing method as described above, a sealing member that is not in contact with the developing sleeve has been proposed to prevent toner from leaking through a gap between a developer container and the longitudinal ends of the developing sleeve to the outside of the developer container. PTL 5 proposes a method in which magnetic sealing members are disposed so as to oppose the ends of the developing sleeve. This is a method in which the magnetic sealing members are disposed at the ends of the developing sleeve with a predetermined gap therebetween, and toner is held by the magnetic sealing members with the magnetic force thereof. In other words, by holding toner that is moving outside the developer container with the magnetic sealing members, leakage of the toner can be prevented.
However, the developing unit has a regulating blade serving as a developer regulating member for regulating the amount of the toner to be born on the developing sleeve to a fixed amount. The magnetic sealing members are disposed outside the regulating blade.
However, it is difficult to make the end faces of the regulating blade and the side faces of the magnetic sealing members close contact with each other because the magnetic sealing members generally have high rigidity. Thus, small gaps may be sometime formed between the end faces of the regulating blade and the magnetic sealing members. The toner born on the developing sleeve in the gaps is located outside the regulating blade and is not regulated by the regulating blade. In other words, the gaps between the end faces of the regulating blade and the magnetic sealing members cause the amount of toner born on the developing sleeve (developer amount) in the gaps to be increased, as compared with that in the other areas. Furthermore, since the toner outside the regulating blade is not subjected to friction due to the regulating blade, the toner resists being charged with electricity, thus having a low electrical charge. Thus, the toner born on the developing sleeve in the areas between the end faces of the regulating blade and the magnetic sealing members can be easily moved from these areas to the photoconductor. Such toner may move to an area of the photoconductor in which no developed image is to be formed, thus causing so-called fogging.
In other words, both of the use of the end sealing members that are in contact with the developing sleeve as sealing members and the use of magnetic sealing members that are not in contact with the developing sleeve may cause the developer born on the developing sleeve to splash or leak.
Furthermore, in the case where the non-contact sealing members are used as sealing members, another sealing member (hot-melt adhesive) is sometimes provided between the magnetic sealing members and the ends of the regulating blade. PTL 6 proposes a method for preventing a developing sleeve from bearing toner outside the ends of the regulating blade by filling the gaps between the magnetic sealing members and the regulating blade with hot melt adhesive.
However, with the contact end sealing members, excessively enhancing the adhesiveness between the end sealing members and the developing sleeve increases the frictional force generated between the developing sleeve and the end sealing members, thus increasing a torque for rotating the developing sleeve. Thus, the developer sealing performance of the end sealing members has to be ensured while the adhesiveness between the developing sleeve and the end sealing members and the torque for rotating the developing sleeve are balanced. This requires sufficiently enhancing the dimensional accuracy of the developing sleeve, the end sealing members, and so on.
Furthermore, with the magnetic sealing members, providing another sealing member (hot-melt adhesive) between the magnetic sealing members and the ends of the regulating blade may increase the cost.